In tall buildings having an enclosed fire escape, known as a fire tower, the occurrence of a fire will often result in smoke entering the fire tower by reason of the opening of doors leading to the fire tower by people attempting to escape a fire or by other means. The presence of smoke in the fire tower is a hazardous condition because it subjects those people who use the fire tower to escape the fire to poor visibility and because they are required to breath smoke-filled air.
A similar problem exists in many industrial applications, such as in clean rooms for the manufacturer of electronic products which would be damaged by the presence of smoke therein, in prisons wherein the prisoners are confined to cells and cannot escape the smoke produced by a fire, in chemical plants where workers can be subjected to exposure to a chemical leak, and in atomic power plants where workers could be subjected to radio-active steam and other radio-active material.
It is apparent there is a need to provide a system for maintaining an enclosed space under a positive pressure fresh air condition in the event of the occurrence of an emergency condition which could introduce hazardous gases or other material into said enclosed space.